A mark is provided on an object surface of an object under measurement, and the mark provides two intersection points P.sub.1 and P.sub.2 between first and second straight lines L.sub.1, L.sub.2, and between second and third lines L.sub.2, L.sub.3, in which an angle ".alpha." defined by the first and...http://www.google.fr/patents/US5901273?utm_source=gb-gplus-shareBrevet US5901273 - Two-dimensional position/orientation measuring mark, two-dimensional position/orientation measuring method and apparatus, control apparatus for image recording apparatus, and control apparatus for manipulator
